1. Field of the Invention
The present invention generally relates to chemical mechanical polishing (CMP) processes and more particularly to an improved process that utilizes a marker with the slurry mixture that more clearly indicates whether the slurry has been completely rinsed from the silicon wafer after the CMP process has been completed.
2. Description of the Related Art
In the manufacture of integrated circuits, semiconductor wafer surface planarity is of extreme importance. To achieve the degree of planarity required to produce ultra high density integrated circuits, chemical-mechanical polishing/planarization (CMP) is often employed. The terms “planarization” and “polishing” as used herein are interchangeable when referring to the technique of “CMP.” In general, CMP involves holding a semiconductor wafer against a moving polishing surface that is wetted with a chemically reactive, abrasive material or slurry, such as silica or alumina. For example, the slurry typically comprises a colloidal suspension of silica particles in a KOH-based solution. The polishing surface is generally a planar pad made of relatively soft, porous material such as blown polyurethane and is usually mounted on a planar platen.
One of the major disadvantages of CMP is the higher defect level observed on post-CMP cleaned wafers. These defects on the semiconductor wafer typically correspond to submicron oxide (e.g., SiO2 or Al2O3) particles from the polishing slurry that remain on the wafer surface after polishing. After CMP, a water rinse and brush scrub are typically employed to remove slurry residue from the surface of the semiconductor wafer. A primary concern with the use of CMP is the efficient and complete removal of the polishing slurry to prevent problems in subsequent processing steps. Commonly used CMP slurries use inorganic oxides such as alumina and silica. If the post-polish cleaning is not sufficient, a layer of the slurry residue will loosely adhere to the product wafer. Slurry residue often becomes detached from wafers during subsequent processing, causing severe foreign matter (FM) problems and defects. Unlike photoresist, the slurry oxides are non-volatile and cannot be detected by a residual gas analyzer (RGA). For example, if the slurry is buried inside metal during sputtering, it will create an electrical short defect after subsequent patterning by reactive ion etching (RIE). Another conventional problem is that the slurry oxides remain on the bevel edges of wafers and are not easily detected by conventional FM inspection tools. Therefore, there is a need for an improved system of detecting the remaining slurry after the wafers have been cleaned. The invention discussed below provides such a system that avoids the above-mentioned problems.